Lubricating oil composition

ABSTRACT

[Problem] 
     To provide a lubricating oil composition capable of attaining high-level fuel efficiency, durability and piston detergency in internal-combustion engines. 
     [Means for Resolution] 
     The lubricating oil composition according to the present invention contains a viscosity index improver and a metallic detergent in at least one base oil selected from mineral oils and synthetic oils therein, wherein the viscosity index improver contains a polymethacrylate viscosity index improver and an olefin copolymer viscosity index improver, the polymethacrylate viscosity index improver is contained in an amount of from 3.0% by mass to 9.5% by mass based on the total amount of the lubricating oil composition, the metallic detergent is at least one selected from calcium sulfonate, calcium phenate and calcium salicylate, the calcium amount derived from the metallic detergent is from 500 ppm to 1500 ppm based on the total amount of the lubricating oil composition, the high-temperature high-shear viscosity at 150° C. of the lubricating oil composition is 2.6 mPa·s or more, the high-temperature high-shear viscosity at 80° C. of the lubricating oil composition is 7.8 mPa·s or less, and the ratio of the high-temperature high-shear viscosity at 100° C. of the lubricating oil composition to the high-temperature high-shear viscosity at 150° C. thereof is 2.05 or less.

TECHNICAL FIELD

The present invention relates to a lubricating oil composition for usein internal-combustion engines such as diesel engines, gasoline engines,gas engines, engines for hybrid cars, etc.

BACKGROUND ART

At present, with the surge of the consciousness for the environment onthe earth scale, implementation of measures against environmental issuessuch as global warming, etc., as well as against depletion of oilresources is desired. In vehicle-related fields, emission control,development of fuel-efficient automobiles and others are much moredesired.

For measures for emission control, employed are exhaust gas filters suchas diesel particulate filters, gasoline particulate filters and the likefor removing metal fractions (also referred to as ash fractions) derivedfrom lubricating oil compositions used in internal-combustion engines,and exhaust-gas aftertreatment devices such as ternary catalysts,oxidation catalysts, etc.

In this case, it is known that metal fractions mix in exhaust gasstreams and deposit in aftertreatment devices to lower the removalefficiency. Accordingly, it is proposed to reduce the content of ametallic additive, especially a metallic detergent, which is containedin a lubricating oil composition for internal-combustion engines (seePatent Literature 1).

In addition, for measures for fuel efficiency improvement, it is nowunder way to control the kinematic viscosity of lubricating oilcompositions for use in internal-combustion engines while maintainingthe balance thereof with wear amount reduction.

In particular, HTHS viscosity indicates a lowered viscosity inhigh-temperature high-shear conditions, and means an effective viscosityon a high-temperature and high-speed slide face. In internal-combustionengines, a lower HTHS viscosity improves fuel efficiency. However, a toolow HTHS viscosity increases a wear amount. Given the situation, it isproposed to control the kinematic viscosity in a temperature rangehaving some influence on fuel consumption while maintaining the balancethereof with resistance to abrasion (see Patent Literature 2).

CITATION LIST Patent Literature [Patent Literature 1] Japanese Patent4965228 [Patent Literature 2] JP-A-2010-280821 SUMMARY OF INVENTIONTechnical Problem

As in Patent Literature 1, reduction in metallic additives such as ametallic detergent, an anti-wear agent and the like results insignificant deterioration of durability and piston detergency that areimportant functions of lubricating oil compositions. Further,deterioration of characteristics of lubricating oil compositions maylower fuel efficiency.

Against deterioration of piston detergency, it may be taken intoconsideration to add an antioxidant or incorporate an ash-freedispersant. However, an ash-free dispersant increases the viscosity oflubricating oil compositions, and is therefore often useless from theviewpoint of fuel efficiency improvement.

As in the above, there is much room for further improvement to satisfythe requirements of fuel efficiency, durability and piston detergency ininternal-combustion engines that are required in late years.

Given the situation, an object of the present invention is to provide alubricating oil composition capable of attaining fuel efficiency,durability and piston detergency in internal-combustion engines at ahigh-level.

Solution to Problem

The present inventors have made assiduous studies and, as a result, havefound that a lubricating oil composition containing a base oil, aviscosity index improver and a metallic detergent, which is socontrolled that the ratio of the high-temperature high-shear viscosityat 100° C. of the lubricating oil composition to the high-temperaturehigh-shear viscosity at 150° C. thereof could be a specific value by theuse of a specific viscosity index improver therein, can solve theabove-mentioned problems, and have completed the present invention.Specifically, the present invention provides the following:

[1] A lubricating oil composition comprising a viscosity index improverand a metallic detergent in at least one base oil selected from mineraloils and synthetic oils therein, wherein the viscosity index improvercontains a polymethacrylate viscosity index improver and an olefincopolymer viscosity index improver, the polymethacrylate viscosity indeximprover is contained in an amount of from 3.0% by mass to 9.5% by massbased on the total amount of the lubricating oil composition, themetallic detergent contains at least one selected from calciumsulfonate, calcium phenate and calcium salicylate, the calcium amountderived from the metallic detergent is from 500 ppm to 1500 ppm based onthe total amount of the lubricating oil composition, thehigh-temperature high-shear viscosity at 150° C. of the lubricating oilcomposition is 2.6 mPa·s or more, the high-temperature high-shearviscosity at 80° C. of the lubricating oil composition is 7.8 mPa·s orless, and the ratio of the high-temperature high-shear viscosity at 100°C. of the lubricating oil composition to the high-temperature high-shearviscosity at 150° C. thereof is 2.05 or less;

[2] The lubricating oil composition according to the above [1], whereinthe NOACK value, as measured in the NOACK test at 250° C. for 1 houraccording to ASTM D 5800, is 13% by mass or less;

[3] The lubricating oil composition according to the above [1] and [2],wherein the polymethacrylate viscosity index improver is anon-dispersant type polymethacrylate viscosity index improver;

[4] The lubricating oil composition according to any of the above [1] to[3], wherein the content of the olefin copolymer viscosity indeximprover is from 30 parts by mass to 250 parts by mass relative to 100parts by mass of the polymethacrylate viscosity index improver;

[5] The lubricating oil composition according to any of the above [1] to[4], wherein the weight-average molecular weight of the polymethacrylateviscosity index improver is from 100,000 to 500,000;

[6] The lubricating oil composition according to any of the above [1] to[5], which contains an antioxidant selected from a phenol-basedantioxidant and an amine-based antioxidant in an amount of from 0.5% bymass to 10% by mass based on the total amount of the lubricating oilcomposition;

[7] A method for producing a lubricating oil composition, whichcomprises:

incorporating a viscosity index improver that contains apolymethacrylate viscosity index improver and an olefin copolymerviscosity index improver so that the amount of the polymethacrylateviscosity index improver is from 3.0% by mass to 9.5% by mass based onthe total amount of the lubricating oil composition,

and a metallic detergent containing at least one selected from calciumsulfonate, calcium phenate and calcium salicylate,

in at least one base oil selected from mineral oils and synthetic oils;

so that the calcium amount derived from the metallic detergent is from500 ppm to 1500 ppm based on the total amount of the lubricating oilcomposition,

that the high-temperature high-shear viscosity at 150° C. of thelubricating oil composition is 2.6 mPa·s or more, that thehigh-temperature high-shear viscosity at 80° C. of the lubricating oilcomposition is 7.8 mPa·s or less,

and that the ratio of the high-temperature high-shear viscosity at 100°C. of the lubricating oil composition to the high-temperature high-shearviscosity at 150° C. thereof is 2.05 or less.

Advantageous Effects of Invention

According to the present invention, there can be provided a lubricatingoil composition capable of attaining fuel efficiency, durability andpiston detergency in internal-combustion engines at a high level.

DESCRIPTION OF EMBODIMENTS Lubricating Oil Composition

The lubricating oil composition of the present invention is alubricating oil composition containing a viscosity index improver and ametallic detergent in at least one base oil selected from mineral oilsand synthetic oils therein, wherein the viscosity index improvercontains a polymethacrylate viscosity index improver and an olefincopolymer viscosity index improver, the metallic detergent contains atleast one selected from calcium sulfonate, calcium phenate and calciumsalicylate, the calcium amount derived from the metallic detergent isfrom 500 ppm to 1500 ppm based on the total amount of the lubricatingoil composition, the high-temperature high-shear viscosity at 150° C. ofthe lubricating oil composition is 2.6 mPa·s or more, thehigh-temperature high-shear viscosity at 80° C. of the lubricating oilcomposition is 7.8 mPa·s or less, and the ratio of the high-temperaturehigh-shear viscosity at 100° C. of the lubricating oil composition tothe high-temperature high-shear viscosity at 150° C. thereof is 2.05 orless.

<Base Oil>

The base oil to be applied to the lubricating oil composition of thisembodiment is at least one selected from mineral oils and syntheticoils, for which any arbitrary one may be suitably selected from mineraloils and synthetic oils used as a base oil in lubricating oilcompositions.

As the mineral oils, for example, there are mentioned mineral oilsprepared by purifying a lubricating oil fraction obtained throughreduced-pressure distillation of an atmospheric residue to be obtainedin atmospheric distillation of a crude oil, through one or moretreatments of solvent deasphalting, solvent extraction, hydrocracking,solvent dewaxing, catalytic dewaxing, hydrorefining, etc., or mineraloils produced through isomerization of wax or GTL wax, etc.

As the synthetic oils, for example, there are mentioned polybutenes,polyolefins [α-olefin homopolymers and copolymers (for example,ethylene-α-olefin copolymers), etc.], various esters (for example,polyol esters, dibasic acid esters, phosphoric acid esters, etc.),various ethers (for example, polyphenyl ethers, etc.), polyglycols,alkylbenzene, alkylnaphthalenes, etc. Of those synthetic oils,especially preferred are polyolefins or polyol esters, from theviewpoint of the high-temperature high-shear viscosity characteristicsthereof and the solubility therein of additives such as viscosity indeximprovers, etc.

In this embodiment, one alone or two or more different types of theabove-mentioned mineral oils may be used either singly or as combined.Also, one alone or two or more different types of the above-mentionedsynthetic oils may be used either singly or as combined. Further, one ormore mineral oils and one or more synthetic oils may be combined. Inparticular, in the lubricating oil composition of the present invention,preferred is combined use of a paraffin mineral oil and apoly-alpha-olefin, from the viewpoint that the NOACK value of thelubricating oil composition, as measured in the NOACK test at 250° C.for 1 hour according to ASTM D 5800, can be readily made to be 13% bymass or less.

The viscosity of the base oil may be selected in accordance with theintended use of the lubricating oil composition, the product grade, etc.The kinematic viscosity at 100° C. of the base oil may be from 2 mm²/sto 30 mm²/s, and is preferably from 2 mm²/s to 15 mm²/s. Morepreferably, the kinematic viscosity is from 2 mm²/s to 10 mm²/s.

When the kinematic viscosity at 100° C. is 2 mm²/s or more, then thevalue loss could be small; and when it is 30 mm²/s or less, then thepower loss owing to viscosity resistance could be inhibited and a fuelefficiency improving effect may be realized.

In the base oil, the paraffin fraction (this may be expressed as %C_(P)) in ring analysis is 70% or more. When % C_(P) is less than 70%,then the oxidation stability is poor so that the acid value may increaseor sludge may form. From these viewpoints, % C_(P) is preferably 80% ormore.

Further, the viscosity index of the base oil is 100 or more, preferably110 or more, more preferably 120 or more. The base oil having aviscosity index of less than 120 could experience a significantviscosity change with changes in temperature, therefore detracting fromfuel efficiency improvement at low temperatures.

<Viscosity Index Improver>

The viscosity index improver applicable to the lubricating oilcomposition of this embodiment includes a polymethacrylate viscosityindex improver and an olefin copolymer viscosity index improver.

(Polymethacrylate Viscosity Index Improver)

As the polymethacrylate viscosity index improver, usable here is anon-dispersant type polymethacrylate viscosity index improver. In thelubricating oil composition of the present invention, preferably used isa non-dispersant type polymethacrylate viscosity index improver, sincethe amount of a deposit which adheres to pistons may be lowered evenunder high-temperature high-shear conditions and therefore pistondetergency may be high.

On the other hand, a dispersant type polymethacrylate viscosity indeximprover is a copolymer produced through addition copolymerization witha nitrogen-containing group as a polar monomer in the molecule, and maytherefore adhere to pistons and others via the polar group to increasethe amount of adhering deposits under high-temperature high-shearconditions.

The polymethacrylate viscosity index improver to be used in thelubricating oil composition of this embodiment includes a non-dispersanttype poly(meth)acrylate compound to be produced throughhomopolymerization of one monomer represented by a general formula (1)or copolymerization of two or more of the monomers represented by ageneral formula (1).

In the above general formula (1), R¹ represents a hydrogen atom or amethyl group, R² represents a linear or branched hydrocarbon grouphaving from 1 to 200 carbon atoms.

The lubricating oil composition of this embodiment of the presentinvention contains a polymethacrylate viscosity index improver in anamount of from 3.0% by mass to 9.5% by mass based on the total amount ofthe lubricating oil composition.

When the content of the polymethacrylate viscosity index improver isless than 3.0% by mass based on the total amount of the lubricating oilcomposition, then the ratio of the high-temperature high-shear viscosityat 100° C. of the lubricating oil composition to the high-temperaturehigh-shear viscosity at 150° C. thereof could not be made to be 2.05 orless.

On the other hand, when the content of the polymethacrylate viscosityindex improver is more than 9.5% by mass, then piston deposits may formand the durability and the piston detergency may lower.

From the viewpoint of easiness in readily making the ratio of thehigh-temperature high-shear viscosity at 100° C. of the lubricating oilcomposition of this embodiment to the high-temperature high-shearviscosity at 150° C. thereof 2.05 or less and in readily improving fuelefficiency, the content of the polymethacrylate viscosity index improveris preferably 4.0% by mass or more, more preferably 6.0% by mass ormore.

From the viewpoint of easiness in improving the durability and thepiston detergency, the content of the polymethacrylate viscosity indeximprover is preferably 9.0% by mass or less, more preferably 8.0% bymass or less.

The polymethacrylate viscosity index improver for use in the presentinvention preferably has a weight-average molecular weight of from100,000 to 500,000, more preferably from 250,000 to 500,000.

Using such a polymethacrylate viscosity index improver that has aweight-average molecular weight falling within the above range, it iseasy to provide the lubricating oil composition in which thehigh-temperature high-shear viscosity at 150° C. is 2.6 mPa·s or more,the high-temperature high-shear viscosity at 80° C. is 7.8 mPa·s orless, and the ratio of the high-temperature high-shear viscosity at 100°C. to the high-temperature high-shear viscosity at 150° C. thereof is2.05 or less.

(Olefin Copolymer Viscosity Index Improver)

As the olefin copolymer viscosity index improver usable in thisembodiment, there are mentioned a styrene-diene hydrogenated copolymer,an ethylene-α-olefin copolymer or its hydrogenated derivative, apolyisobutylene or its hydrogenated derivative, and a polyalkylstyreneor their mixture, etc.

The styrene-diene hydrogenated copolymer is a compound produced byhydrogenating a copolymer of styrene and a diene. The diene usable hereconcretely includes butadiene, isoprene, etc. Especially preferred is ahydrogenated copolymer of styrene and isoprene.

The ethylene-α-olefin copolymer or its hydrogenated derivative is acopolymer of ethylene and an α-olefin or a compound produced byhydrogenating the copolymer. As the α-olefin, concretely, propylene,isobutylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene,1-dodecene, etc. may be used.

The weight-average molecular weight of the olefin copolymer viscosityindex improver is preferably 10,000 or more, more preferably 20,000 ormore, even more preferably 50,000 or more, and is preferably, 800,000 orless, more preferably 600,000 or less, even more preferably 500,000 orless.

The olefin copolymer viscosity index improver having a weight-averagemolecular weight of from 10,000 to 800,000 can realize a sufficientviscosity index improving effect and can be effective for improving fuelefficiency.

In this embodiment, both a polymethacrylate viscosity index improver andan olefin copolymer viscosity index improver are used as combined.

The polymethacrylate viscosity index improver contributes towardlowering the HTHS viscosity at 80° C. to 100° C. of the composition.However, the polymethacrylate viscosity index improver tends to lowerthe piston detergency. Consequently, for example, in internal-combustionengines such as diesel engines that are required to realize high-levelpiston detergency, a polymethacrylate viscosity index improver has notbeen used heretofore.

As opposed to this, in this embodiment, a polymethacrylate viscosityindex improver is positively combined with an olefin copolymer viscosityindex improver to realize the lubricating oil composition beingexcellent in durability without detracting from the piston detergencythereof.

Preferably in the lubricating oil composition of the present invention,the content of the olefin copolymer viscosity index improver is from 30parts by mass to 250 parts by mass relative to 100 parts by mass of thepolymethacrylate viscosity index improver, more preferably from 40 partsby mass to 200 parts by mass, even more preferably from 45 parts by massto 150 parts by mass. Controlling the content of the olefin copolymerviscosity index improver to fall with the above range makes it possibleto reduce the necessary amount of the metallic detergent not increasingthe ash-free dispersant such as succinimide or the like, and thereforerealizes excellent durability and improved piston detergency.

When the content of the olefin copolymer viscosity index improver isfrom 2% by mass to 12.0% by mass based on the total amount of thelubricating oil composition, then a sufficient viscosity index improvingeffect may be realized.

<Metallic Detergent>

The lubricating oil composition of the present invention contains ametallic detergent, the metallic detergent contains at least oneselected from calcium sulfonate, calcium phenate and calcium salicylate,and the calcium amount derived from the metallic detergent is from 500ppm to 1500 ppm based on the total amount of the lubricating oilcomposition of the present invention.

In case where already-existing lubricating oil compositions contain acalcium detergent as a metallic detergent for realizing sufficientdurability and piston detergency, the calcium content therein must be atleast 2000 ppm. However, with emission control being strengthened yearby year, it has become necessary to remove more ash fractions throughexhaust gas filters or in gas aftertreatment devices, and therefore inthe case of using already-existing lubricating oil compositions, theamount of ash fractions depositing on exhaust gas filters or in gasaftertreatment devices may increase.

As opposed to this, the lubricating oil composition of the presentinvention contains, as mentioned above, a polymethacrylate viscosityindex improver and an olefin copolymer viscosity index improver suchthat the high-temperature high-shear viscosity at 150° C. of thelubricating oil composition is 2.6 mPa·s or more, that thehigh-temperature high-shear viscosity at 80° C. of the lubricating oilcomposition is 7.8 mPa·s or less, and that the ratio of thehigh-temperature high-shear viscosity at 100° C. of the lubricating oilcomposition to the high-temperature high-shear viscosity at 150° C.thereof is 2.05 or less, in which the content of the polymethacrylateviscosity index improver is from 3.0% by mass to 9.5% by mass based onthe total amount of the lubricating oil composition, and consequently,even though the metallic detergent in the composition is so reduced thatthe calcium amount derived from the metallic detergent is from 500 ppmto 1500 ppm based on the total amount of the lubricating oilcomposition, the composition can still maintain or even improve thedetergency not requiring increase in the amount of the ash-freedispersant therein.

In the lubricating oil composition of the present invention, the calciumamount is 1500 ppm or less, and therefore the ash fractions that maydeposit on exhaust gas filters or in gas aftertreatment devices can bereduced. Further, metal surface abrasion by calcium can be inhibited.

The lubricating oil composition of the present invention exhibitsexcellent durability and piston detergency even though the calciumcontent therein is 500 ppm. However, calcium may improve durability andpiston detergency, and therefore, the calcium content in the lubricatingoil composition of the present invention is preferably from 700 ppm to1400 ppm based on the total amount of the lubricating oil composition,more preferably from 1000 ppm to 1400 ppm.

As the calcium sulfonate for use in the lubricating oil composition ofthe present invention, there is mentioned a calcium salt of analkyl-aromatic sulfonic acid to be produced by sulfonating analkyl-aromatic compound having a molecular weight of from 300 to 1,500,preferably from 400 to 700.

As the calcium phenate, there are mentioned calcium salts of analkylphenol, an alkylphenol sulfide, and a Mannich reaction product ofan alkylphenol.

As the calcium salicylate, there is mentioned a calcium salt of analkylsalicylic acid.

The alkyl group for constituting the calcium detergent is preferably analkyl group having from 4 to 30 carbon atoms, more preferably havingfrom 6 to 18 carbon atoms, and the group may be linear or branched. Thegroup may be a primary alkyl group, a secondary alkyl group or atertiary alkyl group.

Alkaline earth metal sulfonates, alkaline earth metal phenates andalkaline earth metal salicylates include neutral alkaline earth metalsulfonates, neutral alkaline earth metal phenates and neutral alkalineearth metal salicylates to be produced by directly reacting theabove-mentioned alkyl-aromatic sulfonic acid, alkylphenol, alkylphenolsulfide, Mannich reaction product of alkyl phenol, alkylsalicylic acidor the like with an alkaline earth metal base such as an oxide, ahydroxide or the like of at least one alkaline earth metal selected frommagnesium and calcium.

Calcium sulfonate, calcium phenate and calcium salicylate includeneutral calcium sulfonate, neutral calcium phenate and neutral calciumsalicylate to be produced by once forming the above-mentionedalkyl-aromatic sulfonic acid, alkylphenol, alkylphenol sulfide, Mannichreaction product of alkyl phenol, alkylsalicylic acid or the like intoan alkali metal salt such as a sodium salt, potassium salt or the likethereof followed by substituting the alkali metal of the resultant saltwith calcium.

Further, calcium sulfonate, calcium phenate and calcium salicylateinclude basic calcium metal sulfonate, basic calcium phenate and basiccalcium salicylate to be produced by heating neutral calcium sulfonate,neutral calcium phenate and neutral calcium salicylate along with anexcessive calcium salt or calcium base in the presence of water.

Further, calcium sulfonate, calcium phenate and calcium salicylateinclude overbased calcium sulfonate, overbased calcium phenate andoverbased calcium salicylate to be produced by reacting neutral calciumsulfonate, neutral calcium phenate and neutral calcium salicylate with acalcium carbonate or borate in the presence of carbonic dioxide.

As calcium sulfonate, calcium phenate and calcium salicylate, usablehere are the above-mentioned neutral salt, basic salt, overbased saltand their mixture, etc. In particular, from the viewpoint of calciumreduction, preferred is use of one or more of overbased salicylate,overbased phenate and overbased sulfonate. For realizing excellentdurability and piston detergency as well as abrasion resistance, morepreferred is combined use of one or more of overbased salicylate,overbased phenate and overbased sulfonate, and neutral sulfonate.

The calcium detergent is sold on the market generally in the formthereof diluted with a light lubricant base oil or the like, and iscommercially available. The calcium detergent preferred for use hereinis one having a calcium content of from 1.0% by mass to 20% by mass,more preferably from 2.0% by mass to 16% by mass.

The base value of the calcium detergent is preferably from 10 mg KOH/gto 600 mg KOH/g, more preferably from 20 mg KOH/g to 500 mg KOH/g. Thetotal base value as referred to herein means the total base value in thepotentiometric titration method (base value/perchloric acid method)according to JIS K2501 “7. Test Method for Neutralization Titer forPetroleum Products and Lubricating Oils”.

The metal ratio with respect to the calcium detergent is notspecifically defined. In general, one alone or two or more differentmetallic detergents having a metal ratio of 20 or less may be used hereeither singly or as combined. Preferably, as the essential ingredientthereof, a metallic detergent having a metal ratio of 3 or less, morepreferably 1.5 or less, even more preferably 1.2 or less, can be used,because of excellence in oxidation stability, base value retentivity,high-temperature detergency, and the like. The metal ratio as referredto herein is represented by (number of calcium elementvalences)×(calcium content, mol %)/(soap group content, mol %) in thecalcium detergent, in which the soap group means a sulfonic acid group,a phenol group, a salicylic acid group, or the like, with respect to thecalcium detergent.

The lubricating oil composition of the present invention may contain anyother metallic detergent in addition to the above-mentioned at least oneselected from calcium sulfonate, calcium phenate and calcium salicylate,within a range not detracting from the advantageous effects of thepresent invention.

For example, there are mentioned metallic detergents containing one ormore compounds selected from alkali metal sulfonates, alkali metalphenates, alkali metal salicylates, alkaline earth metal sulfonates,alkaline earth metal phenates and alkaline earth metal salicylates.Preferred is at least any one of alkyl metal sulfonates and alkalineearth metal sulfonates. The alkali metal is preferably sodium, and thealkaline earth metal is preferably magnesium.

<Additives>

If desired and within a range not detracting from the advantageouseffects of the present invention, any other additives such asantioxidant, metallic detergent, viscosity index improver, pour-pointdepressant, rust inhibitor, metal inactivator, defoaming agent,anti-wear agent, extreme-pressure agent and the like may be added to thelubricating oil composition of the present invention.

(Antioxidant)

As antioxidant, usable here is one selected from a phenol-basedantioxidant and an amine-based antioxidant.

The phenol-based antioxidant includes, for example,octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate;4,4′-methylenebis(2,6-di-t-butylphenol); 4,4′-bis(2,6-di-t-butylphenol);4,4′-bis(2-methyl-6-t-butylphenol);2,2′-methylenebis(4-ethyl-6-t-butylphenol);2,2′-methylenebis(4-methyl-6-t-butylphenol);4,4′-butylidenebis(3-methyl-6-t-butylphenol);4,4′-isopropylidenebis(2,6-di-t-butylphenol);2,2′-methylenebis(4-methyl-6-nonylphenol);2,2′-isobutylidenebis(4,6-dimethylphenol);2,2′-methylenebis(4-methyl-6-cyclohexylphenol);2,6-di-t-butyl-4-methylphenol; 2,6-di-t-butyl-4-ethylphenol;2,4-dimethyl-6-t-butylphenol; 2,6-di-t-amyl-p-cresol;2,6-di-t-butyl-4-(N,N′-dimethylaminomethylphenol);4,4′-thiobis(2-methyl-6-t-butylphenol);4,4′-thiobis(3-methyl-6-t-butylphenol);2,2′-thiobis(4-methyl-6-t-butylphenol);bis(3-methyl-4-hydroxy-5-t-butylbenzyl) sulfide;bis(3,5-di-t-butyl-4-hydroxybenzyl)sulfide;n-octyl-3-(4-hydroxy-3,5-di-t-butylphenyl)propionate;n-octadecyl-3-(4-hydroxy-3,5-di-t-butylphenyl)propionate; 2,2′-thio[diethyl-bis-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], etc. Ofthose, especially preferred are a bis-phenol-based antioxidant and anester group-containing phenol-based antioxidant.

The amine-based antioxidant includes, for example,monoalkyldiphenylamines such as monooctyldiphenylamine,monononyldiphenylamine, etc.; dialkyldiphenylamines such as4,4′-dibutyldiphenylamine, 4,4′-dipentyldiphenylamine,4,4′-dihexyldiphenylamine, 4,4′-diheptyldiphenylamine, 4,4′dioctyldiphenylamine, 4,4′-dinonyldiphenylamine, etc.;polyalkyldiphenylamines such as tetrabutyldiphenylamine,tetrahexyldiphenylamine, tetraoctyldiphenylamine,tetranonyldiphenylamine, etc.; naphthylamines, concretelyα-naphthylamine, phenyl-α-naphthylamine and further alkyl-substitutedphenyl-α-naphthylamines such as butylphenyl-α-naphthylamine,pentylphenyl-α-naphthylamine, hexylphenyl-α-naphthylamine,heptylphenyl-α-naphthylamine, octylphenyl-α-naphthylamine,nonylphenyl-α-naphthylamine, etc. Of those, diphenylamines are preferredto naphthylamines, from the viewpoint of the antioxidation effectthereof.

In the present invention, a molybdenum-amine-based antioxidant may befurther added to the composition. As the molybdenum-amine-basedantioxidant, for example, usable here is a product produced by allowinga hexavalent molybdenum compound, concretely molybdenum trioxide and/ormolybdic acid to react with an amine compound, for example, thecompounds to be produced according to the production method described inJP-A 2003-252887.

The amine compound to be reacted with a hexavalent molybdenum compoundis not specifically defined. Concretely, there are mentioned monoamines,diamines, polyamines and alkanolamines. More concretely, there areexemplified alkylamines having an alkyl group with from 1 to 30 carbonatoms (in which the alkyl group may be linear or branched), such asmethylamine, ethylamine, dimethylamine, diethylamine, methylethylamine,methylpropylamine, etc.; alkenylamines having an alkenyl group with from2 to 30 carbon atoms (in which the alkenyl group may be linear orbranched), such as ethenylamine, propenylamine, butenylamine,octenylamine, oleylamine, etc.; alkanolamines having an alkanol groupwith from 1 to 30 carbon atoms (in which the alkanol group may be linearor branched), such as methanolamine, ethanolamine, methanolethanolamine,methanolpropanolamine, etc.; alkylenediamines having an alkylene groupwith from 1 to 30 carbon atoms, such as methylenediamine,ethylenediamine, propylenediamine, butylenediamine, etc.; polyaminessuch as diethylenetriamine, triethylenetetramine,tetraethylenepentamine, pentaethylenehexamine, etc.; compounds having analkyl or alkenyl group having from 8 to 20 carbon atoms on theabove-mentioned monoamines, diamines or polyamines, such asundecyldiethylamine, undecyldiethanolamine, dodecyldipropanolamine,oleyldiethanolamine, oleylpropylenediamine,stearyltetraethylenepentamine, etc.; heterocyclic compounds such asimidazoline, etc.; alkylene oxide-added compounds of those compounds;mixtures of those compounds, etc. In addition, further mentioned aresulfur-containing molybdenum complexes of succinimide and the likedescribed in JP-B 3-22438 and JP-A 2004-2866.

The amount of the antioxidant to be added to the composition ispreferably from 0.5% by mass to 10% by mass based on the total amount ofthe composition, from the viewpoint of the miscibility thereof with baseoil, more preferably from 0.5% by mass to 8% by mass, even morepreferably from 0.5% by mass to 6% by mass, still more preferably from0.5% by mass to 5% by mass. When the antioxidant is in an amount of 0.5%by mass or more based on the total amount of the composition, the acidvalue may be prevented from increasing, and when the antioxidant is inan amount of 5% by mass or less, the solubility in lubricant base oilmay be secured.

(Pour-Point Depressant)

The pour-point depressant includes ethylene-vinyl acetate copolymers,chlorinated paraffin-naphthalene condensates, chlorinatedparaffin-phenol condensates, polymethacrylates, polyalkylstyrenes, etc.For example, preferred for use herein are polymethacrylates having amass-average molecular weight of from 5,000 to 50,000. The amount of thedepressant to be in the composition is from 0.1% by mass to 5% by massbased on the total amount of the composition.

(Rust Inhibitor)

The rust inhibitor includes petroleum sulfonates, alkylbenzenesulfonates, dinonylnaphthalene sulfonates, alkenylsuccinates,polyalcohol esters, etc. The amount of the rust inhibitor is from 0.01%by mass to 1% by mass based on the total amount of the composition,preferably from 0.05% by mass to 0.5% by mass from the viewpoint of theblending effect.

(Metal Inactivator)

The metal inactivator (copper corrosion inhibitor) includesbenzotriazole compounds, tolyltriazole compounds, thiadiazole compounds,imidazole compounds, pyrimidine compounds, etc. Of those, preferred arebenzotriazole compounds. The metal inactivator incorporated in thecomposition can protect engine parts from metallic corrosion andoxidative deterioration. The amount of the metal inactivator to be addedto the composition is preferably from 0.01% by mass to 0.1% by massbased on the total amount of the composition, more preferably from 0.03%by mass to 0.05% by mass, from the viewpoint of the blending effect.

(Defoaming Agent)

The defoaming agent includes silicone oils, fluorosilicone oils,fluoroalkyl ethers, etc. From the viewpoint of the balance between thedefoaming effect and the economic efficiency, the defoaming agent isincorporated in the composition in an amount of from 0.005% by mass to0.1% by mass based on the total amount of the composition.

(Anti-Wear Agent or Extreme-Pressure Agent)

The anti-wear agent or the extreme-pressure agent includessulfur-containing compounds such as zinc dithiophosphate, zincphosphate, zinc dithiocarbamate, molybdenum dithiocarbamate, molybdenumdithiophosphate, disulfides, sulfurized olefins, sulfurized oils andfats, sulfurized esters, thiocarbonates, thiocarbamates, polysulfides,etc.; phosphorus-containing compounds such as phosphites, phosphates,phosphonates, amine salts or metal salts of those compounds, etc.;sulfur and phosphorus-containing anti-wear agents such asthiophosphites, thiophosphates, thiophosphonates, amine salts or metalsalts of those compounds, etc.

In case where the anti-wear agent or extreme-pressure agent isoptionally incorporated in the composition, the amount of the agent ispreferably from 500 ppm by mass to 1000 ppm by mass in terms of the zincelement therein and based on the total weight of the lubricating oilcomposition.

Also preferably, the amount of the anti-wear agent or extreme-pressureagent is from 500 ppm by mass to 1000 ppm by mass in terms of thephosphorus element therein and based on the total weight of thelubricating oil composition, more preferably from 600 ppm by mass to 950ppm by mass, even more preferably from 700 ppm by mass to 950 ppm bymass. The lubricating oil composition of the present invention having azinc content of from 500 ppm by mass to 1000 ppm by mass and aphosphorus content of from 500 ppm by mass to 1000 ppm by mass realizeswear amount reduction and fuel efficiency improvement ininternal-combustion engines.

[Properties of Lubricating Oil Composition]

In the lubricating oil composition of this embodiment, the calciumamount derived from the metallic detergent therein is from 500 ppm to1500 ppm based on the total amount of the lubricating oil composition.

The high-temperature high-shear viscosity at 150° C. of the lubricatingoil composition is 2.6 mPa·s or more. A lubricating oil compositionhaving a high-temperature high-shear viscosity at 150° C. of less than2.6 mPa·s may cause oil film fracture. In addition, the polymer used asa viscosity index improver may fracture to provide permanent viscosityreduction that would be unrestorable even when the temperature of thelubricating oil composition lowers.

The high-temperature high-shear viscosity at 80° C. of the lubricatingoil composition is 7.8 mPa·s or less. Using a lubricating oilcomposition having a high-temperature high-shear viscosity at 80° C. ofmore than 7.8 mPa·s, the fuel efficiency of internal-combustion enginesin a temperature range of 80° C. would worsen.

The ratio of the high-temperature high-shear viscosity at 100° C. of thelubricating oil composition to the high-temperature high-shear viscosityat 150° C. thereof must be 2.05 or less.

When the ratio of the high-temperature high-shear viscosity at 100° C.of the lubricating oil composition to the high-temperature high-shearviscosity at 150° C. thereof is 2.05 or less, then the composition canmaintain or improve the detergency thereof not requiring increase in theamount of the ash-free dispersant therein, even when the amount of themetallic detergent therein is reduced so that the calcium amount derivedfrom the metallic detergent is from 500 ppm to 1500 ppm based on thetotal amount of the lubricating oil composition.

The high-temperature high-shear viscosity of the lubricating oilcomposition at 150° C. is 2.6 mPa·s or more and the ratio of thehigh-temperature high-shear viscosity at 100° C. to the high-temperaturehigh-shear viscosity at 150° C. thereof is more than 2.05. This meansthat the viscosity resistance at 100° C. of the composition is large. Inother words, when a lubricating oil composition has a ratio of thehigh-temperature high-shear viscosity at 100° C. to the high-temperaturehigh-shear viscosity at 150° C. thereof of more than 2.05, fuelefficiency in a temperature range of 100° C. worsens.

When the ratio of HTHS viscosity at 100° C. to HTHS viscosity at 150° C.is lowered too much, then the detergency of the composition worsens, andtherefore, the lower limit of the ratio HTHS viscosity at 100° C. toHTHS viscosity at 150° C. is 1.80.

The high-temperature high-shear viscosity at 150° C. of the lubricatingoil composition and the high-temperature high-shear viscosity at 100° C.thereof coming to be close to each other, that is, the ratio coming tobe nearer to 1 means that the viscosity resistance of the composition at100° C. can be lowered. In this case, for example, fuel efficiency inrunning in a medium speed range can be increased.

Preferably, the lubricating oil composition of this embodiment is suchthat the NOACK value thereof, as measured in the NOACK test at 250° C.for 1 hour according to ASTM D 5800, is 13% by mass or less. When havingan NOACK value of 13% by mass or less, the consumption of thelubricating oil composition can be reduced and therefore sludge wouldhardly form.

From this viewpoint, the NOACK value is more preferably 12% by mass orless, even more preferably 11% by mass or less. From the viewpoint thatthe consumption reducing effect of the lubricating oil composition wouldreach a ceiling, the lower limit of the NOACK value is 6% by mass.

Irrespective of the structures of the polymethacrylate viscosity indeximprover and the olefin copolymer viscosity index improver therein andusing both the two, the lubricating oil composition of this embodimentis so planned that the high-temperature high-shear viscosity at 80° C.thereof is 7.8 mPa·s or less, that the high-temperature high-shearviscosity at 150° C. thereof is 2.6 mPa·s or more and that the ratio ofthe high-temperature high-shear viscosity at 100° C. to thehigh-temperature high-shear viscosity at 150° C. thereof is 2.05 orless, and therefore exhibits excellent fuel efficiency, durability andpiston detergency.

<Phosphorus Content and Sulfate Ash Content in Lubricating OilComposition>

The phosphorus content in the lubricating oil composition of the presentinvention is preferably from 500 ppm by mass to 1000 ppm by mass basedon the total amount of the lubricating oil composition. Having aphosphorus content of from 500 ppm by mass to 1000 ppm by mass, thecomposition attains sufficientanti-wear performance. From thisviewpoint, the phosphorus content is more preferably from 600 ppm bymass to 950 ppm by mass, even more preferably from 700 ppm by mass to950 ppm by mass.

The sulfate ash content in the lubricating oil composition of thepresent invention is preferably from 0.4% by mass to 0.8% by mass basedon the total amount of the composition. Having a sulfate ash contentfalling within the range, the composition realizes reduction in theamount of ash to deposit on DPF filters when applied to diesel enginesand therefore prevents DPF filters from clogging with ash to therebycontribute toward prolongation of the life of DPF filters.

The sulfate ash content means the ash content as determined by addingsulfuric acid to the carbonized residue formed in burning a samplefollowed by heating it to have a constant weight, and is generally usedas an index of indicating the approximate amount of the metallicadditives in lubricating oil compositions. Concretely, the sulfate ashcontent is measured according to the method defined in JIS K 2272 “5.Test Method for Sulfate Ash Content”.

Examples

The present invention is described in more detail with reference to thefollowing Examples. The present invention is not limited to thefollowing Examples.

[Properties Measurement of Lubricating Oil Composition] (1) KinematicViscosity (at 40° C. and 100° C.)

Measured according to ASTM D445.

(2) Viscosity Index of Base Oil

Measured according to “Test Method for Kinematic Viscosity of PetroleumProducts” defined in JIS K 2283.

(3) CCS Viscosity of Composition

Measured according to ASTM D2602.

(4) NOACK Value of Composition

Measured according to ASTM D5800.

(5) HTHS Viscosity (High-Temperature High-Shear Viscosity), at 80° C.,100° C., 150° C.

Measured according to ASTM D4683.

(6) Phosphorus and Calcium Content

Measured according to JPI-5S-38-92.

[Properties Evaluation] <Panel Coking Test>

300 ml of a sample oil was heated in a heating tank at 100° C., andsplashed on an aluminium plate arranged on the top of the heating tankand heated at 300° C. using feathers, and this operation was continuedfor 3 hours. After 3 hours, the mass of the deposit adhering to thealuminium plate was measured.

<Residual Base Value after ISOT>

Measured according to JIS K2514.

<Shell Four-Ball Test>

Measured according to ASTM D2783.

<Engine Motoring Torque Test>

A commercially-available 1.8-liter engine was driven with an externalmotor, and the torque necessary for the driving was measured. Regardingthe oil/water temperature of the lubricating oil composition chargedinside the engine, the oil temperature and the water temperature wereset at 80° C. on the assumption of actual running.

The engine rotation number was set at 1500 rpm, and the torque at therotation number was measured. It is considered that, when the measuredengine driving torque is smaller, the fuel efficiency of the chargedlubricating oil composition is better.

Examples and Comparative Examples

Using a base oil, a dispersant, a metallic detergent and otheradditives, sample oils of lubricating oil compositions of Examples 1 and2 and Comparative Examples 1 to 4 were prepared, and according to theabove-mentioned evaluation methods, these sample oils were measured forthe characteristics and the properties thereof. The results are shown inTable 1. Lubricating oil compositions of Examples 3 and 4 andComparative Examples 5 and 6 were prepared in the same manner as inExample 1 except for changing the calcium amount based on the totalamount of the lubricating oil composition, and according to theabove-mentioned evaluation methods, these were measured for thecharacteristics and the properties thereof. The results are shown inTable 2. For comparison, the results of Example 2 are shown in Table 2.

Table 3 shows the ratio of the high-temperature high-shear viscosity at100° C. of different lubricating oil compositions, which had beenprepared using different PMA viscosity index improvers, to thehigh-temperature high-shear viscosity at 150° C. thereof.

TABLE 1 Comparative Comparative Comparative Comparative Example 1Example 2 Example 1 Example 2 Example 3 Example 4 Lubricating OilMineral Oil*¹ (mass %) balance balance balance balance balance balanceComposition Synthetic Oil*² (mass %) 10.00 10.00 10.00 10.00 10.00 10.00PMA Vixocosity Index Improver*³ (mass %) 4.80 7.20 0.00 2.40 9.60 12.00OCP Viscosity Index*⁴ (mass %) 10.40 6.20 17.70 13.90 3.10 0.00 MetallicDetergent*⁵ (mass %) 2.36 2.36 2.36 2.36 2.36 2.36 Additive Package*⁶(mass %) 12.25 12.25 12.25 12.25 12.25 12.25 Properties 40° C. KinematicViscosity Index (mm²/s) 36.5 35.0 39.0 37.8 34.2 33.8 100° C. KinematicViscosity Index (mm²/s) 8.0 7.8 8.2 8.1 7.7 7.7 Viscosity Index 201 203192 196 205 208 CCS Viscosity (mPa · s) ≦6200 ≦6200 ≦6200 ≦6200 ≦6200≦6200 NOACK Test (mass %) ≦13 ≦13 ≦13 ≦13 ≦13 ≦13 HTHS Viscosity 80° C.(mPa · s) 7.7 7.2 8.2 7.9 6.8 6.5 HTHS Viscosity 100° C. (mPa · s) 5.35.1 5.5 5.4 4.9 4.8 HTHS Viscosity 150° C. (mPa · s) 2.6 2.6 2.6 2.6 2.62.6 Phosphorus Content (mass %) 0.09 0.09 0.09 0.09 0.09 0.09 (based onlubricating oil composition) Calcium* (mass %) 0.12 0.12 0.12 0.12 0.120.12 (based on lubricating oil composition) Ratio of 100° C. HTHSViscosity 2.04 1.96 2.12 2.08 1.88 1.85 to 150° C. HTHS ViscosityEvaluation Engine Motoring Torque Reduction Nm 8.29 8.27 8.34 8.31 8.248.24 Results Torque Reduction % 0.60 0.84 0.00 0.36 1.20 1.20 PanelCoking Test mg 84 95 67 79 120 127 Residual Base Value after ISOT mgKOH/g — 0.67 — — — — Shell Four-Ball Test mm — 0.38 — — — —

TABLE 2 Comparative Comparative Example 2 Example 3 Example 4 Example 5Example 6 Lubricating Oil Mineral Oil*¹ (mass %) balance balance balancebalance balance Composition Synthetic Oil*² (mass %) 10.00 10.00 10.0010.00 10.00 PMA Viscosity Index Improver*³ (mass %) 7.20 7.20 7.20 7.207.20 OCP Viscosity Index*⁴ (mass %) 6.20 6.20 6.20 6.20 6.20 MetallicDetergent*⁵ (mass %) 2.36 0.98 2.95 0.00 3.93 Additive Package*⁶ (mass%) 12.25 12.25 12.25 12.25 12.25 Properties 40° C. Kinematic ViscosityIndex (mm²/s) 35.0 34.5 35.8 34.0 36.4 100° C. Kinematic Viscosity Index(mm²/s) 7.8 7.7 7.9 7.6 8.0 Viscosity Index 203 202 202 202 202 CCSViscosity (mPa · s) ≦6200 ≦6200 ≦6200 ≦6200 ≦6200 NOACK Test (mass %)≦13 ≦13 ≦13 ≦13 ≦13 HTHS Viscosity 80° C. (mPa · s) 7.2 7.2 7.4 7.2 7.4HTHS Viscosity 100° C. (mPa · s) 5.1 5.1 5.2 5.1 5.2 HTHS Viscosity 150°C. (mPa · s) 2.6 2.6 2.6 2.6 2.6 Phosphorus Content (mass %) 0.09 0.090.09 0.09 0.09 (based on lubricating oil composition) Calcium Content(mass %) 0.12 0.05 0.15 0.00 0.20 (based on lubricating oil composition)Ratio of 100° C. HTHS Viscosity to 1.96 1.96 2.00 1.96 2.00 150° C. HTHSViscosity Evaluation Engine Motoring Torque Reduction Nm 8.27 — — — —Results Torque Reduction % 0.84 — — — — Panel Coking Test mg 95 — — — —Residual Base Value after ISOT mg KOH/g 0.67 0.31 0.95 0.00 1.31 ShellFour-Ball Test mm 0.38 0.37 0.38 0.36 0.45

TABLE 3 Comparative Comparative Example 7 Example 8 Example 5Lubricating Oil Mineral Oil *¹ (mass %) balance balance balanceComposition Synthetic Oil *² (mass %) 10.00 10.00 10.00 PMA ViscosityIndex Improver *⁷ (mass %) 10.70 0.00 0.00 PMA Viscosity Index Improver*⁸ (mass %) 0.00 7.76 0.00 PMA Viscosity Index Improver *⁹ (mass %) 0.000.00 8.44 OCP Viscosity Index Improver *⁴ (mass %) 3.1 3.1 3.1 MetallicDetergent *⁵ (mass %) 2.36 2.36 2.36 Additive Package *⁶ (mass %) 12.2512.25 12.25 Properties 40° C. Kinematic Viscosity (mm²/s) 37.5 38.9 36.8100° C. Kinematic Viscosity (mm²/s) 7.9 8.4 8.3 Viscosity Index 189 201211 CCS Viscosity (mPa · s) ≦6200 ≦6200 ≦6200 NOACK Test (mass %) ≦13≦13 ≦13 HTHS Viscosity 80° C. (mPa · s) 11.0 7.9 6.5 HTHS Viscosity 100°C. (mPa · s) 6.6 5.4 4.8 HTHS Viscosity 150° C. (mPa · s) 2.6 2.6 2.6Phosphorus Content (mass %) 0.09 0.09 0.09 (based on lubricating oilcomposition) Calcium Content (mass %) 0.12 0.12 0.12 (based onlubricating oil composition) Ratio of 100° C. HTHS Viscosity to 2.542.08 1.85 150° C. HTHS Viscosity

Notes in Table 1 and Table 2 are as follows:

*1: Paraffinic mineral oil: grade 100 N (40° C. kinematic viscosity 17.9mm²/s, 100° C. kinematic viscosity 4.1 mm²/s, viscosity index 131, %Cp=87.4%, density 0.825 g/cm³)*2: PAO: poly-alpha-olefin (40° C. kinematic viscosity 25.1 mm²/s, 100°C. kinematic viscosity 5.1 mm²/s, viscosity index 141, density 0.824g/cm³)*3: PMA viscosity index improver (non-dispersant type polymethacrylatepolymer, Mw=370,000)*4: OCP viscosity index improver (non-dispersant type olefin copolymerpolymer, Mw=100,000)*5: Neutral calcium sulfonate, overbased calcium phenate*6: The additive package is an additive prepared by removing themetallic detergent from a package according to ACEA/C2, JASO DL-1Standards. This contains ZnDTP (Prim. +Sec type) as anti-wear agent,polymer bis-type imide as dispersant, diphenylamine and hindered phenolas antioxidant, benzotriazole as metal inactivator, and siliconedefoaming agent as defoaming agent.*7: PMA viscosity index improver (non-dispersant type polymethacrylatepolymer, Mw=30,000)*8: PMA viscosity index improver (non-dispersant type polymethacrylatepolymer, Mw=200,000)*9: PMA viscosity index improver (non-dispersant type polymethacrylatepolymer, Mw=420,000)

[Evaluation Results]

From the results shown in Table 1 and Table 2, it can be seen that, whenthe ratio of the HTHS viscosity at 100° C. of the lubricating oilcomposition to the HTHS viscosity at 150° C. thereof is 2.05 or less,then the degree of torque reduction (that is, rate of improvement) ishigh, and the composition contributes toward increasing fuel efficiency.

From the results shown in Table 3, it can be seen that, by changing thetype of the PMA viscosity index improver, the ratio of thehigh-temperature high-shear viscosity at 100° C. of the lubricating oilcomposition to the high-temperature high-shear viscosity at 150° C.thereof can be controlled.

From the above, it can be seen that the lubricating oil composition ofthe present invention satisfies high-level fuel efficiency anddurability.

INDUSTRIAL APPLICABILITY

The lubricating oil composition of the present invention is favorablyused as a lubricating oil composition for internal-combustion engineshaving, as mounted thereon, any of exhaust gas filters such as dieselparticulate filters, gasoline particulate filters and the like andexhaust-gas aftertreatment devices such as ternary catalysts, oxidationcatalysts, etc.

1. A lubricating oil composition comprising a viscosity index improverand a metallic detergent in at least one base oil selected from mineraloils and synthetic oils therein: wherein the viscosity index improvercontains a polymethacrylate viscosity index improver and an olefincopolymer viscosity index improver, the polymethacrylate viscosity indeximprover is contained in an amount of from 3.0% by mass to 9.5% by massbased on the total amount of the lubricating oil composition, themetallic detergent contains at least one selected from calciumsulfonate, calcium phenate and calcium salicylate, the calcium amountderived from the metallic detergent is from 500 ppm to 1500 ppm based onthe total amount of the lubricating oil composition, thehigh-temperature high-shear viscosity at 150° C. of the lubricating oilcomposition is 2.6 mPa·s or more, the high-temperature high-shearviscosity at 80° C. of the lubricating oil composition is 7.8 mPa·s orless, and the ratio of the high-temperature high-shear viscosity at 100°C. of the lubricating oil composition to the high-temperature high-shearviscosity at 150° C. thereof is 2.05 or less.
 2. The lubricating oilcomposition according to claim 1, wherein the NOACK value, as measuredin the NOACK test at 250° C. for 1 hour according to ASTM D 5800, is 13%by mass or less.
 3. The lubricating oil composition according to claim1, wherein the polymethacrylate viscosity index improver is anon-dispersant type polymethacrylate viscosity index improver.
 4. Thelubricating oil composition according to claim 1, wherein the content ofthe olefin copolymer viscosity index improver is from 30 parts by massto 250 parts by mass relative to 100 parts by mass of thepolymethacrylate viscosity index improver.
 5. The lubricating oilcomposition according to claim 1, wherein the weight-average molecularweight of the polymethacrylate viscosity index improver is from 100,000to 500,000.
 6. The lubricating oil composition according to claim 1,which comprises an antioxidant selected from a phenol-based antioxidantand an amine-based antioxidant in an amount of from 0.5% by mass to 10%by mass based on the total amount of the lubricating oil composition. 7.A method for producing a lubricating oil composition, which comprises:incorporating a viscosity index improver that contains apolymethacrylate viscosity index improver and an olefin copolymerviscosity index improver so that the amount of the polymethacrylateviscosity index improver is from 3.0% by mass to 9.5% by mass based onthe total amount of the lubricating oil composition, and a metallicdetergent containing at least one selected from calcium sulfonate,calcium phenate and calcium salicylate, in at least one base oilselected from mineral oils and synthetic oils: so that the calciumamount derived from the metallic detergent is from 500 ppm to 1500 ppmbased on the total amount of the lubricating oil composition, that thehigh-temperature high-shear viscosity at 150° C. of the lubricating oilcomposition is 2.6 mPa·s or more, that the high-temperature high-shearviscosity at 80° C. of the lubricating oil composition is 7.8 mPa·s orless, and that the ratio of the high-temperature high-shear viscosity at100° C. of the lubricating oil composition to the high-temperaturehigh-shear viscosity at 150° C. thereof is 2.05 or less.